Vacuum evacuation apparatus

ABSTRACT

The present invention relates to a vacuum evacuation apparatus which can be mounted in a posture that can freely be selected a vacuum evacuation apparatus for evacuating a container from an atmospheric pressure to a high vacuum or less includes a first vacuum pump for evacuating the container to a high vacuum or less, and a second vacuum pump for evacuating the container from an atmospheric pressure to a medium or low vacuum the first vacuum pump and the second vacuum pump are integrally connected to each other into an integral unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This document claims priority to Japanese Patent Application No.2012-080559, filed on Mar. 30, 2012, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum evacuation apparatus which iscapable of compressing a gas from an ultrahigh vacuum to an atmosphericpressure, and more particularly to a vacuum evacuation apparatus whichcan be mounted in a posture that can freely be selected.

2. Description of the Related Art

Conventionally, in a semiconductor fabrication apparatus or the like, acombination of a turbomolecular pump and a dry vacuum pump has been usedfor evacuating a gas in a chamber to create a clean ultrahigh vacuum inthe chamber. The turbomolecular pump serves to evacuate the chamber toan ultrahigh vacuum range, and the dry vacuum pump serves to evacuatethe chamber in a range from an atmospheric pressure to a medium vacuum.The turbomolecular pump and the dry vacuum pump are driven by respectivepower supplies and individually controlled in operation.

The turbomolecular pump and the dry vacuum pump are thus used as vacuumpumps in different vacuum ranges. When a turbomolecular pump is used, itis necessary to initially use a dry vacuum pump to evacuate the chamberto a rough vacuum range, i.e., a medium vacuum range, in which theturbomolecular pump can be used to further evacuate the chamber.Therefore, it is essential to install the dry vacuum pump as a roughingvacuum pump in order to use the turbomolecular pump.

As one advanced concept of the turbomolecular pump, an atmosphericpressure-evacuation-type turbomolecular pump which can evacuate thechamber from an atmospheric pressure range has been proposed. However,such turbomolecular pump has not yet been fully developed into apractically feasible product on account of various problems aboutrequirements for mechanical strength of a rotor that needs to rotate atultrahigh speeds, radiation of the heat of a compressed gas produced atthe time of evacuation from an atmospheric pressure range to anultrahigh vacuum range, the structure of a motor that needs largetorques and ultrahigh-speed rotation, and a driving power supply source.

Heretofore, in order to create an ultrahigh vacuum, it has been thegeneral practice to use a positive displacement vacuum pump such as anoil rotary pump, a roots dry pump, or a screw dry pump which is capableof creating a vacuum in the range from several Torr to 10⁻² Torr, and akinetic vacuum pump (turbomolecular pump) or an entrapment vacuum pump(cryopump), disposed upstream of the positive displacement vacuum pump,for creating an ultrahigh vacuum (see Japanese laid-open patentpublication Nos. 11-40094, 2000-131476 and 2002-147386). Specifically,two vacuum pumps are connected in series with each other for creating anultrahigh vacuum. The positive displacement vacuum pump is mostlyinstalled or placed on an installation surface such as a ground surface,and the kinetic vacuum pump or the entrapment vacuum pump is installedin the vicinity of a vacuum container (vacuum chamber) to be evaluatedto an ultrahigh vacuum or is directly connected to the vacuum container(vacuum chamber). The vacuum pump that is installed in the vicinity ofthe vacuum container or is directly connected to the vacuum container isreferred to as a first vacuum pump, and the vacuum pump that isinstalled or placed on the installation surface such as a ground surfaceis referred to as a second vacuum pump. The second vacuum pump is notinstalled in the vicinity of the vacuum container because of itsvibrations or noise or because it uses oil, but is installed at a remotelocation, e.g., at a downstairs installation site. Therefore, the secondvacuum pump is connected to the first vacuum pump by a long vacuumpiping. As a result, the second vacuum pump needs to have evacuationcapacity in view of the conductance of the vacuum piping, i.e., to havelarger capacity as required by the conductance of the vacuum piping.

Vacuum pumps having a single rotational shaft which can compress a gasfrom an ultrahigh vacuum to an atmospheric pressure are disclosed in thefollowing documents:

1) Japanese laid-open patent publication No. 60-204997:

The disclosed vacuum pump is a kinetic vacuum pump, which includes ahelical screw pump section and a centrifugal pump section, forcompressing a gas from an ultrahigh vacuum to an atmospheric pressure.Since turbine blades and centrifugal blades are mounted in series on onerotational shaft, the centrifugal blades which are located at anatmospheric pressure side have a poor evacuation efficiency in theatmospheric pressure range, and thus the vacuum pump requires largedriving power.

2) Japanese patent No. 2680156:

The disclosed vacuum pump is a kinetic vacuum pump, which includes acentrifugal compression pump stage and a circumferential flowcompression pump stage, for compressing a gas from an ultrahigh vacuumto an atmospheric pressure. Since centrifugal blades and vortex flowblades are mounted in series on one rotational shaft, the vortex flowblades which are located at an atmospheric pressure side have a poorevacuation efficiency in the atmospheric pressure range, and thus thevacuum pump requires large driving power.

The problems of the related art in which a single vacuum pump cancompress a gas from an ultrahigh vacuum to an atmospheric pressure aresummarized as follows: The use of blades having different evacuationprinciples provided on the same rotational shaft causes a problem oflimitations of evacuation performance, and the use of kinetic vacuumpump section having a poor evacuation efficiency in an atmosphericpressure range causes a problem of increased driving power.

SUMMARY OF THE INVENTION

As described above, in a vacuum evacuation apparatus having two vacuumpumps connected in series, i.e., a positive displacement vacuum pump anda kinetic vacuum pump which can compress a gas from an ultrahigh vacuumto an atmospheric pressure, because the positive displacement vacuumpump has a good evacuation efficiency in an atmospheric pressure range,a highly efficient evacuation system can be realized. However, thedisplacement vacuum pump cannot be installed in the vicinity of a vacuumcontainer (vacuum chamber) because of its vibrations, heat generatedwhen a gas is compressed to an atmospheric pressure, and the like.

Further, a single vacuum pump which is capable of compressing a gas froman ultrahigh vacuum to an atmospheric pressure has a problem oflimitations of evacuation performance and a problem of increased drivingpower.

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide a vacuumevacuation apparatus which is capable of compressing a gas from anultrahigh vacuum to an atmospheric pressure, simplifying an evacuationsystem and reducing a driving power for higher efficiency, and can beinstalled in any desired directions in the vicinity of a vacuumcontainer or directly on the vacuum container.

In order to achieve the above object, according to a first aspect of thepresent invention, there is provided a vacuum evacuation apparatus forevacuating a container from an atmospheric pressure to a high vacuum orless, comprising: a first vacuum pump for evacuating the container to ahigh vacuum or less; and a second vacuum pump for evacuating thecontainer from an atmospheric pressure to a medium or low vacuum;wherein the first vacuum pump and the second vacuum pump are integrallyconnected to each other into an integral unit.

Here, the high vacuum means a pressure range from 0.1 to 10⁻⁵ Pa. Themedium vacuum means a pressure range from 100 to 0.1 Pa. The low vacuummeans a pressure range from a pressure lower than the atmosphericpressure to 100 Pa. Further, an ultrahigh vacuum means a pressure rangefrom 10⁻⁵ to 10⁻⁸ Pa. An extrahigh vacuum means a pressure lower than10⁻⁸ Pa. A vacuum that can be created on the earth is about 10⁻¹⁰ Pa atpresent.

According to the present invention, the first vacuum pump and the secondvacuum pump are integrally connected to each other, and hence it ispossible for the user to evacuate a gas in a container to an ultrahighvacuum by a single pump system. Since the first vacuum pump forevacuating a gas in the container to a high vacuum or less and thesecond vacuum pump for evacuating the gas in the container from anatmospheric pressure to a medium or low vacuum are combined with eachother, it is possible for the respective pumps to consume appropriateamounts of power respectively in the medium vacuum range and theultrahigh vacuum range. Therefore, there is provided a pump system thatdoes not essentially operate in a low evacuation efficiency state, i.e.,a state where evacuation in the ultrahigh vacuum range is performed by asingle pump comprising a positive vacuum pump or a state whereevacuation in the atmospheric pressure range is performed by a singlepump comprising a kinetic vacuum pump.

The expression “the first vacuum pump and the second vacuum pump areintegrally connected to each other into an integral unit” means that thefirst vacuum pump and the second vacuum pump are coupled and integratedinto a physically single pump unit. In this case, a controller forcontrolling the whole pumps in the vacuum evacuation apparatus may bemounted on the pump unit or may be installed in the vicinity of the pumpunit. In the case where the first vacuum pump and the second vacuum pumpare coupled and integrated, the first vacuum pump and the second vacuumpump may be directly coupled or a coupling member may be providedbetween the first vacuum pump and the second vacuum pump.

In a preferred aspect of the present invention, the first vacuum pumphas a rotational shaft and the second vacuum pump has a rotationalshaft, and the rotational shaft of the first vacuum pump and therotational shaft of the second vacuum pump have respective axes whichare perpendicular to each other.

When the first vacuum pump and the second vacuum pump are in operation,they produce vibrations in substantially the same directions, i.e.,their vibrational energies are intensive in substantially the samedirections. Specifically, the first vacuum pump and the second vacuumpump produce vibrations due to unbalanced rotating bodies in the radialdirections of their rotational shafts. If the rotational shaft of thesecond vacuum pump and the rotational shafts of the first vacuum pump inthe unitized vacuum evacuation apparatus according to the presentinvention are disposed parallel to each other, then it is possible forthe second vacuum pump and the first vacuum pump to simultaneouslyproduce rotary vibrations in the radial directions perpendicular to theaxes of the rotational shafts, causing resonant vibrations and causingimpairment of pump mechanical components. If such radial vibrations aregenerated, they tend to be added to each other and the added vibrationsare transmitted as excessive vibrations to the vacuum container side.According to the present invention, the axes of the rotational shafts ofthe first vacuum pump and the axis of the rotational shaft of the secondvacuum pump extend perpendicularly to each other, thereby minimizingradial vibrations generated by the rotational shaft of the first vacuumpump that is attached to the vacuum container.

In a preferred aspect of the present invention, the first vacuum pumphas a rotational shaft and the second vacuum pump has a rotationalshaft, and the rotational shaft of the first vacuum pump and therotational shaft of the second vacuum pump are rotatably supported byone of self-lubricating bearings, bearings having a semi-solid lubricantor a solid lubricant therein, gas bearings, and magnetic bearings; andwherein the rotational shaft of the first vacuum pump and the rotationalshaft of the second vacuum pump are rotatable regardless of directionsin which the first vacuum pump and the vacuum pump are installed.

According to the present invention, the bearings that support therotational shaft of the first vacuum pump and the bearings that supportthe rotational shafts of the second vacuum pump may comprise rollingbearings made of a self-lubricating material or including grease inroller races, self-lubricating journal bearings, or non-contact bearingssuch as gas bearings or magnetic bearings. These bearings allow therotational shafts to rotate in stable conditions regardless of mountingdirections of the vacuum evacuation apparatus. Since the vacuumevacuation apparatus according to the present invention has anappearance as a single pump unit, the user does not usually think thatit contains the first vacuum pump and the second vacuum pump combinedtogether. The dry vacuum pumps used generally for a second vacuum pumpuses low-viscosity lubricating oil such as mineral oil to lubricate thebearings, and hence has certain limitations on the mounting directionsthereof. On the other hand, the turbomolecular pump has its rotationalshaft rotatably supported by ball bearings that are lubricated mainly bygrease, or non-contact bearings, so that the turbomolecular pump is freeof limitations with respect to directions in which it is mounted. Thedry vacuum pump according to the present invention uses the bearingswhich can support the rotational shafts without using low-viscositylubricating oil such as mineral oil, and thus does not pose limitationson the mounting directions of the pump unit.

In a preferred aspect of the present invention, the first vacuum pumphas a bottom component and the second vacuum pump has a casing, and thebottom component and the casing are integrally connected to each other,thereby integrally connecting the first vacuum pump and the secondvacuum pump.

According to the present invention, the bottom component of the firstvacuum pump and the pump casing of the second vacuum pump are integratedinto a common part, and an evacuation passage is provided in the commonpart to allow the first vacuum pump and the second vacuum pump tocommunicate with each other. Thus, the number of parts used is reducedand hence the cost thereof is reduced, and the overall unit takes up areduced volume. By incorporating the evacuation path of the two pumpsinto the common part, the evacuation path of the two pumps can beshortened to increase the conductance of the pump unit, and the volumeof the second vacuum pump can be reduced. Then, the cost of the entirepump unit can be further reduced and the volume taken up by the entirepump unit can be reduced. Furthermore, since the bottom component andthe pump casing are integrated, thermal conductivity of the two pumpscan be improved. The second vacuum pump which compresses a gas up to theatmospheric pressure consumes more electric power and generates moreheat than the first vacuum pump at the ultrahigh vacuum side. If thesecond vacuum pump is cooled by cooling water, the increased thermalconductivity between the two pumps allows only a cooling mechanismincorporated in the first vacuum pump to cool the two pumps efficiently(to radiate heat from the two pumps efficiently).

In a preferred aspect of the present invention, the first vacuum pumpand the second vacuum pump are integrally connected to each otherthrough a heat insulation member or a small area of contact.

If the second vacuum pump is not cooled by cooling water, then in orderto lower the thermal conductivity between the fastening surfaces of thefirst vacuum pump and the second vacuum pump, it is effective to combinea thermal insulation with the fastening portion or to reduce thecross-sectional area of a contacting region of the fastening portion, orboth to combine a thermal insulation with the fastening portion and toreduce the cross-sectional area of a contacting region of the fasteningportion. If the second vacuum pump is not cooled by cooling water, thenit is forcedly air-cooled. The second vacuum pump which compresses a gasup to the atmospheric pressure consumes more electric power andgenerates more heat than the first vacuum pump. If the second vacuumpump is forcedly air-cooled, its exhaust heat performance is much lowerthan the cooling water. If the thermal conductivity between the twopumps is high, the heat may be transferred from the second vacuum pumpto the first vacuum pump, possibly impairing the normal operation of thefirst vacuum pump. Therefore, by providing the heat insulation member atthe connecting portion of the two pumps or making the contact area ofthe connecting portion small, the thermal conductivity between the twopumps is lowered to minimize the heat transfer from the second vacuumpump to the first vacuum pump.

In a preferred aspect of the present invention, the first vacuum pumpand the second vacuum pump are integrally connected to each otherthrough a vibro-isolating mechanism.

The second vacuum pump which compresses a gas up to the atmosphericpressure vibrates to an extent greater than the first vacuum pump. Ifvibrations of the vacuum evacuation apparatus of the present inventionwhich integrates the first vacuum pump and the second vacuum pump arelarge, the vacuum evacuation apparatus cannot be installed in thevicinity of the vacuum container. Therefore, the vibro-isolatingmechanism for isolating vibrations from the second vacuum pump isprovided at the connecting portion of the first vacuum pump and thesecond vacuum pump, and thus any vibrations that are transmitted fromthe second vacuum pump to the first vacuum pump can be reduced. Thevibro-isolating mechanism may comprise a vibro-isolating rubber (naturalrubber, nitrile rubber, silicone rubber, fluoro rubber, etc.) which hasa Young's modulus equal to or smaller than 1000 KPa (1000 to 10 KPa) andan Asker C hardness level equal to or smaller than 50 (50 to 4), or maycomprise a spring.

In a preferred aspect of the present invention, the first vacuum pumphas an outlet port and the second vacuum pump has an inlet port, and theoutlet port and the inlet port are interconnected by an evacuationpassage component comprising a vibro-isolating material.

If the evacuation passage component is made of a highly rigid materialor has a highly rigid structure, then it may transmit vibrations fromthe second vacuum pump to the first vacuum pump. Since the evacuationpassage component is made of a vibro-isolating material, it can minimizevibrations transmitted from the second vacuum pump to the first vacuumpump. The vibro-isolating material may be a rubber material (naturalrubber, nitrile rubber, silicone rubber, fluoro rubber, etc.) which hasa Young's modulus equal to or smaller than 1000 KPa (1000 to 10 KPa) andan Asker C hardness level equal to or smaller than 50 (50 to 4), and maybe in the shape of a tube or a block.

In a preferred aspect of the present invention, the first vacuum pumphas an inlet port and the second vacuum pump has an inlet port, and theinlet port of the first vacuum pump and the inlet port of the secondvacuum pump are interconnected by a bypass passage for bypassing thefirst vacuum pump.

According to the present invention, the bypass pipe which interconnectsthe inlet port of the first vacuum pump and the inlet of the secondvacuum pump is provided. The bypass pipe serves to directly discharge agas from the inlet port of the first vacuum pump into the inlet of thesecond vacuum pump, thereby bypassing the first vacuum pump.Consequently, even when the vacuum in the vacuum container breaks, asudden load buildup can be prevented from being exerted on the firstvacuum pump, and hence the rotating body of the first vacuum pump can beprotected against damage.

In a preferred aspect of the present invention, the first vacuum pumphas an outlet port and the second vacuum pump has an inlet port, and theoutlet port and the inlet port are interconnected by an evacuationpassage component incorporating therein a check valve for preventing afluid from flowing back from the second vacuum pump to the first vacuumpump while the first vacuum pump is in operation.

According to the present invention, the first vacuum pump and the secondvacuum pump are integrally connected together into an integral pump unitincluding the evacuation passage component therein. Therefore, thepressure conditions for the evacuation passage component are known. Whenone of the first and second vacuum pumps fails to operate, e.g., whenthe second vacuum pump becomes faulty in operation, the back pressure ofthe first vacuum pump increases suddenly. By providing the check valvewhich automatically closes under the differential pressure in theevacuation passage component, the pressure at the exhaust side of thefirst vacuum pump can be prevented from abruptly rising.

In a preferred aspect of the present invention, further comprising acontroller for controlling the first vacuum pump and the second vacuumpump wherein the controller is integrally connected to the first vacuumpump or is installed separately from the first vacuum pump.

In a preferred aspect of the present invention, when each of the firstvacuum pump and the second vacuum pump reaches a rated rotational speedand no gas is introduced into the container, the controller lowers avoltage applied to a motor of at least one of the first vacuum pump andthe second vacuum pump and continuously operates the motor at a motormaximum efficient point.

In a preferred aspect of the present invention, the controller iscapable of controlling the pressure in the container at a targetpressure level by individually controlling respective rotational speedsof the first vacuum pump and the second vacuum pump depending on flowrates of the gas evacuated therefrom.

With the first vacuum pump and the second vacuum pump that areintegrally connected into an integral unit, passage pipes combined withthe integral unit and having given diameters and lengths remainunchanged or constant. In the event of changes in the rotational speedsof the first vacuum pump and the second vacuum pump, the flow rate andthe pressure change with regularity.

Usually, the evacuation rate of a pump is controlled by adjusting theopening area of the suction side with a control valve or the like.According to the present invention, however, the pressure in the vacuumcontainer to be evacuated is controlled by controlling at least one ofthe rotational speed of the first vacuum pump and the rotational speedof the second vacuum pump, rather than by adjusting the opening (openingarea) of a valve disposed between the vacuum container and the pump. Inthis manner, the evacuation rate of each of the vacuum pumps is adjustedto adjust the overall evacuation rate of the pump system as the vacuumevacuation apparatus. In other words, the pressure in the vacuumcontainer can be controlled by the single pump system without the needfor a control valve other than the vacuum pumps.

In a preferred aspect of the present invention, wherein the first vacuumpump comprises a turbomolecular pump, and the second vacuum pumpcomprises a dry vacuum pump.

In a preferred aspect of the present invention, the second vacuum pumpcomprises a dry vacuum pump having a pair of pump rotors with respectivemagnet rotors mounted thereon, the magnet rotors have equal numbers ofmagnetic poles and are disposed so that their different magnetic polesare magnetically attracted to each other, and currents supplied to amultiphase armature including an iron core and a plurality of windingsdisposed radially outwardly of at least one of the magnet rotors areswitched to actuate the at least one of the magnet rotors for therebyrotating the pump rotors in opposite directions in synchronism with eachother.

According to the present invention, the dual-shaft pump rotors can berotated synchronously in the opposite directions by a simple structuralmotor having permanent magnets and windings for rotating the permanentmagnets. Therefore, any timing gears for synchronizing the dual-shaftpump rotors are not required, and oil-free, low vibrations and low noisecan be realized. If lubricating oil is used to lubricate the bearingsand timing gears, the lubricating oil leaks out when the pump is tilted,and hence mounting posture of the pump is limited. However, the oil-freepump according to the present invention can be mounted in a posture thatcan freely be selected, and does not produce significant vibrations andnoise caused by contact of the timing gears.

Since the dry vacuum pump having the above structure is used as thesecond vacuum pump, any vibrations that are transmitted from the secondvacuum pump to the first vacuum pump can be suppressed, and thus thesecond vacuum pump can be integrally coupled to the first vacuum pump.When the first vacuum pump and the second vacuum pump are integrallycoupled to each other, the second vacuum pump can be mounted at a freelyselectable posture. Furthermore, when the integral unit of the firstvacuum pump and the second vacuum pump is attached to an object to beevacuated, e.g., a vacuum container (vacuum chamber), the integral unitcan be mounted at a freely selectable posture.

In a preferred aspect of the present invention, one of the first vacuumpump and the second vacuum pump comprises a single vacuum pump and theother of the first vacuum pump and the second vacuum pump compriseseither a single vacuum pump or a plurality of vacuum pumps.

In a preferred aspect of the present invention, the first vacuum pumpand the second vacuum pump are integrally connected to each other by atleast one evacuation passage.

According to the present invention, since the plural second vacuum pumpsare integrally connected to the single first vacuum pump, it is possibleto construct a roughening pump system having an evacuation capacitywhich matches the evacuation capacity of the first vacuum pump. Sincethe plural second vacuum pumps can be controlled in parallel forcontrolling the pressure in the vacuum container, the pressure in thevacuum container can be controlled more appropriately. Further, even ifone of the second vacuum pumps fails to operate, the other second vacuumpump can back up the first vacuum pump. Therefore, even if one of thesecond vacuum pumps shuts down, a situation where the first vacuum pumpshuts down to cause a quick pressure buildup in the vacuum container canbe avoided.

A plurality of the first vacuum pumps may be integrally connected to asingle second vacuum pump. With this arrangement, the rotor of each ofthe first vacuum pumps can be reduced in size. Two or three vacuum pumpsthat are integrally connected to each other can be controlled by asingle controller.

In a preferred aspect of the present invention, the ratio of an axialdimension of the second vacuum pump and an axial dimension, which isassumed to be 1, of the first vacuum pump is in a range from 1 to 0.6,and the ratio of a volume of the second vacuum pump and a volume, whichis assumed to be 1, of the first vacuum pump is in a range from 0.3 to0.5.

Since the second vacuum pump can be smaller in size than the firstvacuum pump, there is no limitation on the mounting posture when thesecond vacuum pump is mounted on the first vacuum pump.

By using the combination of the above dimension and volume ratios forthe first vacuum pump and the second vacuum pump, it is possible tointegrally connect a plurality of second vacuum pumps to the firstvacuum pump which has an evacuation capacity that is several timesgreater than each of the second vacuum pumps.

The present invention offers the following advantages:

(1) By integrating a first vacuum pump for evacuating the container to ahigh vacuum or less and a second vacuum pump for evacuating thecontainer from an atmospheric pressure to a medium or low vacuum,ultrahigh vacuum evacuation can be performed by a single pump system.Further, by a combination of the first vacuum pump for evacuating thecontainer to a high vacuum or less and the second vacuum pump forevacuating the container from an atmospheric pressure to a medium or lowvacuum, the pumps can evacuate the container respectively to the mediumvacuum range and the ultrahigh vacuum range by appropriate respectiveconsumed power, and the consumed power of the whole system can bereduced.

(2) Since the second vacuum pump as an auxiliary pump can be integrallycoupled to the first vacuum pump, the installation space (footprint) ofthe auxiliary pump can be reduced.

(3) When the first vacuum pump and the second vacuum pump are integrallycoupled to each other, the second vacuum pump can be mounted at a freelyselectable posture. Furthermore, when the integral unit of the firstvacuum pump and the second vacuum pump is attached to an object to beevacuated, e.g., a vacuum container (vacuum chamber), the integral unitcan be mounted at a freely selectable posture.

(4) The pressure in the vacuum container to be evacuated is controlledby controlling at least one of the rotational speed of the first vacuumpump and the rotational speed of the second vacuum pump, rather than byadjusting the opening (opening area) of a valve disposed between thevacuum container and the pump. Therefore, the evacuation rate of each ofthe vacuum pumps is adjusted to adjust the overall evacuation rate ofthe pump system. In other words, the pressure in the vacuum containercan be controlled by the single pump system without the need for acontrol valve or the like.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front elevational view, partly in cross section, of avacuum evacuation apparatus according to a first aspect of the presentinvention;

FIG. 1B is a side elevational view, partly in cross section, of thevacuum evacuation apparatus shown in FIG. 1A;

FIG. 1C is a bottom view, partly in cross section, of the vacuumevacuation apparatus shown in FIG. 1A;

FIG. 2 is a schematic cross-sectional view showing structural details ofa first vacuum pump of the vacuum evacuation apparatus shown in FIG. 1A;

FIG. 3 is a schematic cross-sectional view showing structural details ofa second vacuum pump of the vacuum evacuation apparatus shown in FIG.1A;

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3;

FIG. 5A is a front elevational view, partly in cross section, of thevacuum evacuation apparatus with the second vacuum pump being installedat another posture;

FIG. 5B is a side elevational view, partly in cross section, of thevacuum evacuation apparatus shown in FIG. 5A;

FIG. 5C is a bottom view, partly in cross section, of the vacuumevacuation apparatus shown in FIG. 5A;

FIGS. 6A and 6B are front elevational views of the vacuum evacuationapparatus with a controller mounted on the first vacuum pump indifferent positions;

FIGS. 7A and 7B are schematic cross-sectional views showing a vacuumevacuation apparatus in which a bottom component of the first vacuumpump and a pump casing of the second vacuum pump are integrally joinedto each other;

FIG. 8 is a schematic front elevational view, partly in cross section,of a vacuum evacuation apparatus in which a vibro-isolating mechanism isprovided between the first vacuum pump and the second vacuum pump

FIG. 9 is a schematic front elevational view, partly in cross section,of a vacuum evacuation apparatus in which a fastening component forfastening the first vacuum pump and the second vacuum pump is combinedwith a vibro-isolating mechanism;

FIG. 10A is a cross-sectional view of the structure of a fasteningassembly comprising the fastening component and vibro-isolating bushingsshown in FIG. 9;

FIG. 10B is a bottom view of the fastening assembly shown in FIG. 10A;

FIG. 10C is an exploded perspective view of one of the vibro-isolatingbushings shown in FIG. 10A;

FIGS. 11A and 11B are front elevational views of a pump unit (vacuumevacuation apparatus) having a first vacuum pump and a second vacuumpump that are integrally mounted on a vacuum container (vacuum chamber);

FIG. 12A is a front elevational view, partly in cross section, of avacuum evacuation apparatus with a second vacuum pump mounted on a sidesurface of a first vacuum pump;

FIG. 12B is a bottom view of the vacuum evacuation apparatus with thesecond vacuum pump mounted on the side surface of the first vacuum pump;

FIGS. 13A and 13B are a front elevational view, partly in cross section,and a bottom view of a vacuum evacuation apparatus with a second vacuumpump mounted on a side surface of a first vacuum pump, the first vacuumpump and the second vacuum pump being fastened to each other by afastening component combined with a vibro-isolating mechanism;

FIG. 13C is a cross-sectional view showing structural details of afastening assembly of the vacuum evacuation apparatus shown in FIGS. 13Aand 13B;

FIG. 14 is a schematic front elevational view of a vacuum evacuationapparatus including a first vacuum pump, a second vacuum pump, and acheck valve disposed in a evacuation passage component whichinterconnects an outlet port of the first vacuum pump and an inlet portof the second vacuum pump;

FIG. 15 is a schematic front elevational view of a vacuum evacuationapparatus including a first vacuum pump, a second vacuum pump, and abypass pipe interconnecting an inlet port of the first vacuum pump andan inlet port of the second vacuum pump for bypassing the first vacuumpump;

FIG. 16 is a set of graphs showing comparison results in which therotational speeds of first and second vacuum pumps were changed toadjust the pressure in a vacuum container in a pump rotational speedcontrol process which was performed on a vacuum evacuation apparatusaccording to the present invention and a vacuum evacuation apparatusaccording to the related art, in the case of the first vacuum pumpcomprising a turbomolecular pump and the second vacuum pump comprising adry pump;

FIG. 17 is a schematic front elevational view, partly in cross section,of a vacuum evacuation apparatus according to an embodiment of thepresent invention which includes a single first vacuum pump and aplurality of second vacuum pumps integrally connected to the firstvacuum pump;

FIG. 18 is a schematic front elevational view, partly in cross section,of a vacuum evacuation apparatus according to an embodiment of thepresent invention which includes a single first vacuum pump and aplurality of second vacuum pumps integrally connected to the firstvacuum pump by inlet and outlet passages;

FIG. 19 is a schematic front elevational view, partly in cross section,of a vacuum evacuation apparatus according to an embodiment of thepresent invention which includes a plurality of first vacuum pumps and asingle second vacuum pump integrally connected to the first vacuum pumpsby inlet and outlet passages;

FIG. 20 is a block diagram of a control circuit for controlling a vacuumevacuation apparatus including two first vacuum pumps and a singlesecond vacuum pump which are integrally connected;

FIG. 21 is a graph showing how the rotational speeds of a single firstvacuum pump and two second vacuum pumps were changed to adjust thepressure in a vacuum container in a pump rotational speed controlprocess which was performed on a vacuum evacuation apparatus accordingto the present invention, in the case of the first vacuum pumpcomprising a turbomolecular pump and the two second vacuum pumpscomprising a dry pump;

FIG. 22 is a cross-sectional view of a turbomolecular pump for use in avacuum evacuation apparatus according to the present invention;

FIG. 23 is a cross-sectional view of another turbomolecular pump for usein a vacuum evacuation apparatus according to the present invention;

FIG. 24 is a cross-sectional view of still another turbomolecular pumpfor use in a vacuum evacuation apparatus according to the presentinvention; and

FIG. 25 is a cross-sectional view of yet another turbomolecular pump foruse in a vacuum evacuation apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vacuum evacuation apparatus according to preferred embodiments of thepresent invention will be described in detail below with reference toFIGS. 1A through 25. Identical or corresponding parts are denoted byidentical or corresponding reference characters throughout views.

FIGS. 1A, 1B and 1C are views showing a vacuum evacuation apparatusaccording to a first aspect of the present invention, FIG. 1A is a frontelevation view, partly in cross section, FIG. 1B is a side elevationalview, partly in cross section, and FIG. 1C is a bottom view, partly incross section.

As shown in FIGS. 1A, 1B and 1C, according to an embodiment of thepresent invention, a vacuum evacuation apparatus is configured toevacuate a vacuum container (vacuum chamber) from an atmosphericpressure to an ultrahigh vacuum range. The vacuum evacuation apparatuscomprises a first vacuum pump 1 capable of evacuating the container to ahigh vacuum or less and a second vacuum pump 2 capable of evacuating thecontainer to a pressure ranging from an atmospheric pressure to a mediumor low vacuum. The first vacuum pump 1 and the second vacuum pump 2 areunitized as an integral apparatus. Specifically, the first vacuum pump 1and the second vacuum pump 2 are coupled together into an integral unit.The first vacuum pump 1 comprises a turbomolecular pump, and the secondvacuum pump 2 comprises a dry vacuum pump. An outlet port of the firstvacuum pump 1 and an inlet port of the second vacuum pump 2 areinterconnected by an evacuation passage component 3.

For evacuating a gas in a certain container from an atmospheric pressurerange to an ultrahigh vacuum range, normally, a positive displacementpump (e.g., dry pump) as a second vacuum pump is initially used toevacuate the container to a medium vacuum range, and then aturbomolecular pump as a first vacuum pump is activated to evacuate thecontainer to an ultrahigh vacuum range, thus performing evacuationoperation. According to the conventional method, the second vacuum pump(e.g., dry pump) for evacuating the container to a medium vacuum and thefirst vacuum pump (e.g., turbomolecular pump) for evacuating thecontainer to an ultrahigh vacuum range are separately prepared, andconnected together by a piping, thus constructing an evacuating systemwhich is capable of performing a series of evacuation. However, in thismethod, depending on the length and diameter of the piping used tointerconnect the dry pump and the turbomolecular pump, even though thecontainer to be evacuated remains unchanged, the evacuation time andpower required for evacuation tend to vary, and even the pumpsthemselves may need to be changed. Consequently, special engineeringexpertise is often required in evacuating equipment planning.

According to the present invention, the first vacuum pump 1 comprising aturbomolecular pump and the second vacuum pump 2 comprising a dry vacuumpump are integrated and unitized. Thus, the user can construct andperform ultrahigh vacuum evacuation in a container by a single pumpsystem. By a combination of the turbomolecular pump and the dry vacuumpump, the pumps can evacuate the container respectively to the mediumvacuum range and the ultrahigh vacuum range by appropriate respectiveconsumed power. Therefore, according to the present invention, there isprovided a pump system that does not essentially operate in a lowevacuation efficiency state, i.e., a state where evacuation in theultrahigh vacuum range is performed by a single pump comprising apositive vacuum pump or a state where evacuation in the atmosphericpressure range is performed by a single pump comprising a kinetic vacuumpump.

The expression “the first vacuum pump 1 and the second vacuum pump 2 arecoupled together into an integral unit” means that the first vacuum pump1 and the second vacuum pump 2 are coupled and integrated into aphysically single pump unit, as shown in FIG. 1A. In this case, acontroller for controlling the whole pumps in the vacuum evacuationapparatus may be mounted on the pump unit or may be installed in thevicinity of the pump unit.

As shown in FIGS. 1A, 1B and 1C, the second vacuum pump 2 comprises ascrew-type dry vacuum pump having a pair of screw rotors 52 a, 52 brotatably disposed in a pump casing (described below).

FIG. 2 is a schematic cross-sectional view showing structural details ofthe first vacuum pump 1 of the vacuum evacuation apparatus shown inFIGS. 1A through 1C.

As shown in FIG. 2, the turbomolecular pump as the first vacuum pump 1comprises a pump casing 9, and a turbine blade pumping assembly 10 and athread groove pumping assembly 20 which are disposed in the pump casing9 and successively arranged from an inlet port side to an outlet portside of the turbomolecular pump. The turbine blade pumping assembly 10comprises a plurality of turbine blades 11 as an array of multistagerotor blades and multistage stator blades 14 disposed immediatelydownstream of the corresponding turbine blades 11. The multistageturbine blades 11 are integrally formed on a substantially cylindricalrotor 12 fixedly mounted on a rotational shaft 13 that is rotatablydisposed centrally in the pump casing 9. The multistage stator blades 14are held between spacers 15 stacked in the pump casing 9 and are fixedin the pump casing 9. The turbine blades 11 as rotor blades and thestator blades 14 are alternately disposed in the turbine blade pumpingassembly 10.

The thread groove pumping assembly 20 comprises cylindrical threadgrooves 21 disposed on an outer circumferential surface of thecylindrical rotor 12, and a cylindrical thread groove spacer 22 disposedso as to face the outer circumferential surfaces of the cylindricalthread grooves 21. The thread groove spacer 22 is fixed to the pumpcasing 9.

The turbomolecular pump also includes a stator 25 disposed in the rotor12. The stator 25 has a base 26 fixed to a lower flange 91 f of the pumpcasing 9 and a sleeve 27 extending axially upwardly from the base 26.The sleeve 27 of the stator 25 supports a bearing motor assembly 30including a motor 31 for applying rotational drive forces to therotational shaft 13 and bearings 32, 33, 34 for rotatably supporting therotational shaft 13.

The bearing motor assembly 30 comprises a motor 31 for applyingrotational drive forces to the rotational shaft 13, an upper radialmagnetic bearing 32 for radially supporting the rotational shaft 13, alower radial magnetic bearing 33 for radially supporting the rotationalshaft 13, and a thrust magnetic bearing 34 for canceling thrust forcesgenerated by the pressure difference developed between the inlet sideand the outlet side by evacuation operation of the evacuation assembles.The motor 31 comprises a high-frequency motor. Each of the upper radialmagnetic bearing 32, the lower radial magnetic bearing 33, and thethrust magnetic bearing 34 comprises an active magnetic bearing.

The pump casing 9 has an upper flange 9 uf on its upper end. The inletport SP is defined radially inwardly of the upper flange 9 uf. A vacuumcontainer (vacuum chamber) to be evacuated by the vacuum evacuationapparatus is connected to the upper flange 9 uf. Further, the base 26 ofthe stator 25 has a flange 26 f, and the outlet port DP is definedradially inwardly of the flange 26 f. The evacuation passage component 3(see FIG. 1) is connected to the flange 26 f, and the first vacuum pump1 comprising a turbomolecular pump communicates with the second vacuumpump 2 by the evacuation passage component 3.

FIG. 3 is a schematic cross-sectional view showing structural details ofthe second vacuum pump 2 of the vacuum evacuation apparatus shown inFIGS. 1A through 1C. As shown in FIG. 3, the second vacuum pump 2comprises a screw-type dry vacuum pump. The second vacuum pump 2comprises a pump casing 50, and two parallel rotational shafts 51 a, 51b disposed in the pump casing 50. The rotational shafts 51 a, 51 b arerotatably supported by respective pairs of bearings 53. The rotationalshaft 51 a supports a screw rotor 52 a fixed thereto which has aright-hand screw thread, and the rotational shaft 51 b supports a screwrotor 52 b fixed thereto which has a left-hand screw thread. The screwrotors 52 a, 52 b are juxtaposed in alignment with each other betweenthe bearings 53 which support the rotational shafts 51 a, 51 b.

As shown in FIG. 3, small clearances are defined between outercircumferential surfaces of the screw rotors 52 a, 52 b and an innercircumferential surface of the pump casing 50, allowing the screw rotors52 a, 52 b to rotate out of contact with the pump casing 50. The screwrotors 52 a, 52 b have mutually confronting regions where the right- andleft-hand screw threads loosely mesh with each other to allow the screwrotors 52 a, 52 b to rotate out of contact with each other. Magnetrotors 54 are fixed respectively to ends of the rotational shafts 51 a,51 b. The pump casing 50 has an inlet port SP and an outlet port DP thatare formed in a side wall thereof which lies parallel to the sheet ofFIG. 3. The inlet port SP of the second vacuum pump 2 is connected tothe outlet port DP of the first vacuum pump 1 by the evacuation passagecomponent 3 (see FIG. 1). The bearings 53 which are remote from themagnet rotors 54 are fixed to the pump casing 50, and the other bearings53 which are close to the magnet rotors 54 are fixed to a bearinghousing 55 and a bearing holder 56. The bearing housing 55 is fixed tothe pump casing 50, and the bearing holder 56 is fixed to the bearinghousing 55.

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3. Asshown in FIG. 4, the magnet rotors 54 are identical in structure anddisposed parallel to each other. Each of the magnet rotors 54 includes ayoke 54 b made of a magnetic material and a ring-shaped magnet 54 amounted on the outer circumferential surface of the yoke 54 b. Thering-shaped magnet 54 a is magnetized into eight poles, so that eachmagnet rotor 54 has eight magnetic poles on its outer circumferentialsurface. Though each magnet rotor 54 is shown as a structure havingeight magnetic poles in the illustrated embodiment, the number of themagnetic poles should be an even number of magnetic poles (2n: n=1, 2, .. . ). The magnet rotors 54 are disposed in facing relation to eachother with their different magnetic poles being magnetically attractedto each other, and are disposed so as to keep a clearance C definedtherebetween. The screw rotors 52 a, 52 b are capable of rotatingsmoothly in opposite directions in synchronism with each other becauseof a magnetic coupling between the magnet rotors 54. In order toincrease forces for synchronously rotating the screw rotors 52 a, 52 b,a plurality of pairs of magnet rotors 54 may be mounted on therotational shafts 51 a, 51 b.

The screw-type dry vacuum pump includes two armatures 57 for generatingforces to rotate the magnet rotors 54. Each of the armatures 57 is of athree-phase (U, V, W) configuration with an iron core 57 a and threewindings 57 b which are disposed in the vicinity of a portion of theouter circumferential surface of one of the magnet rotors 54. The twoarmatures 57 are mounted on inner walls of the pump casing 50 remotefrom the region where the magnet rotors 54 face each other. The magneticforces which attract the magnet rotors 54 to each other are canceled byattractive forces that act between the magnet rotors 54 and the ironcores 57 a. Adjacent two of the windings 57 b in the respective phasesof each of the armatures 57 are angularly spaced from each other by 60degrees about the rotational shaft 51 a or 51 b.

The windings 57 b in the phases, that are denoted by U₁, V₁, W₁, U₁′,V₁′, W₁′, and the iron cores 57 a of the armatures 57, and the magnetrotors 54 jointly make up a dual-shaft synchronous brushless DC motor.The windings 57 b in the phases U₁′, V₁′, W₁′ are coiled in the oppositedirection to the windings 57 b in the phases U₁, V₁, W₁. Depending onthe positions of the magnetic poles of the magnet rotors 54, sixcurrents I_(UV), I_(VW), I_(WU), I_(VU), I_(WP), I_(UW) flowing throughthe respective windings 57 b in the phases U₁, V₁, W₁, U₁′, V₁′, W₁′ areswitched to rotate the magnet rotors 54.

The screw-type dry vacuum pump shown in FIGS. 3 and 4 is capable ofrotating the two screw rotors 52 a, 52 b synchronously in the oppositedirections by a simple structural motor having permanent magnets andwindings for rotating the permanent magnets. Therefore, the screw-typedry vacuum pump does not need any timing gears for synchronizing the twoscrew rotors 52 a, 52 b, and hence is free of lubricating oil andrealizes low vibrations and low noise. If lubricating oil is used tolubricate the bearings and timing gears, the lubricating oil leaks outwhen the pump is tilted, and hence mounting posture of the pump islimited. However, the oil-free pump according to the present inventioncan be mounted in a posture that can freely be selected, and does notproduce significant vibrations and noise caused by contact of the timinggears.

Since the screw-type dry vacuum pump having the above structure is usedas the second vacuum pump 2, any vibrations that are transmitted fromthe second vacuum pump 2 to the first vacuum pump 1 can be suppressed,and thus the second vacuum pump 2 can be integrally coupled to the firstvacuum pump 1. When the first vacuum pump 1 and the second vacuum pump 2are integrally coupled to each other, the second vacuum pump 2 can bemounted at a freely selectable posture. Furthermore, when the integralunit of the first vacuum pump 1 and the second vacuum pump 2 is attachedto an object to be evacuated, e.g., a vacuum container (vacuum chamber),the integral unit can be mounted at a freely selectable posture.

A mounting posture for mounting the second vacuum pump 2 shown in FIGS.3 and 4 on the first vacuum pump 1 will be described below withreference to FIGS. 1A through 1C. As shown in FIGS. 1A through 1C, thesecond vacuum pump 2 is mounted on the first vacuum pump 1 with the twoscrew rotors 52 a, 52 b being juxtaposed parallel to the lower surfaceof the first vacuum pump 1. Specifically, the screw rotors 52 a, 52 b ofthe second vacuum pump 2 have respective axes 52 ax, 52 bx which areperpendicular to the axis 1 x of the rotational shaft 13 of the firstvacuum pump 1 and spaced by the same distance from the lower surface ofthe first vacuum pump 1.

FIGS. 5A, 5B and 5C are views showing another examples of mountingpostures in the case where the second vacuum pump 2 is mounted on thefirst vacuum pump 1, FIG. 5A is a front elevational view, partly incross section, FIG. 5B is a side elevational view, partly in crosssection, and FIG. 5C is a bottom view, partly in cross section.

As shown in FIGS. 5A through 5C, the second vacuum pump 2 is mounted onthe first vacuum pump 1 with the two screw rotors 52 a, 52 b beingjuxtaposed parallel to the lower surface of the first vacuum pump 1.Specifically, the screw rotors 52 a, 52 b of the second vacuum pump 2have respective axes 52 ax, 52 bx which are perpendicular to the axis 1x of the rotational shaft 13 of the first vacuum pump 1 and verticallyspaced one above the other from the lower surface of the first vacuumpump 1.

In the vacuum evacuation apparatus shown in FIGS. 1 and 5, the firstvacuum pump 1 comprising a turbomolecular pump and the second vacuumpump 2 comprising a dry vacuum pump are integrally connected togetherinto an integral unit, and the second vacuum pump 2 have respectiverotational shafts whose axes lying perpendicularly to the axis of therotational shaft of the first vacuum pump 1.

When the dry vacuum pump and the turbomolecular pump are in operation,they produce vibrations in substantially the same directions, i.e.,their vibrational energies are intensive in substantially the samedirections. Specifically, the dry vacuum pump and the turbomolecularpump produce vibrations due to unbalanced rotating bodies in the radialdirections of their rotational shafts. If the rotational shaft of theturbomolecular pump and the rotational shafts of the dry vacuum pump inthe unitized vacuum evacuation apparatus according to the presentinvention are disposed parallel to each other, then it is possible,though very small probability, for the turbomolecular pump and the dryvacuum pump to simultaneously produce rotary vibrations in the radialdirections perpendicular to the axes of the rotational shafts, causingresonant vibrations. If such radial vibrations are generated, they tendto be added to each other and the added vibrations are transmitted asexcessive vibrations to the vacuum container side. According to thepresent invention, the axes of the rotational shafts of the dry vacuumpump and the axis of the rotational shaft of the turbomolecular pumpextend perpendicularly to each other, thereby minimizing radialvibrations generated by the rotational shaft of the first vacuum pumpthat is attached to the vacuum container.

As described above, the turbomolecular pump that is generally used asthe first vacuum pump can be mounted at a freely selectable posture, andhence can be installed in any desired orientation on the vacuumcontainer. Therefore, the turbomolecular pump as the first vacuum pumpmakes a great contribution to the degree of freedom of design around thevacuum container. When the two pumps are combined together into a pumpunit for use as the vacuum evacuation apparatus according to the presentinvention, the axis 1 x of the first vacuum pump 1 to be directlyattached to the vacuum container is held in alignment with the center ofgravity of the unitized vacuum evacuation apparatus. If the vacuumevacuation apparatus is installed in a horizontal orientation, then notorsional moment occurs around the axis 1 x of the first vacuum pump 1,allowing the vacuum container with the vacuum evacuation apparatusinstalled thereon to be deformed in a simplified manner or allowing theinstallation process to be simplified. The vibrations produced by thevacuum evacuation apparatus do not include torsional vibrations, andhence can easily be suppressed. It is important to suppress vibrationsbecause the vacuum evacuation apparatus is installed in the vicinity ofthe vacuum container or is connected directly to the vacuum container.

The bearings that support the rotational shaft of the first vacuum pump1 and the bearings that support the rotational shafts of the secondvacuum pump 2 may comprise rolling bearings made of a self-lubricatingmaterial or including grease in roller races, self-lubricating journalbearings, or non-contact bearings such as gas bearings or magneticbearings. These bearings allow the rotational shafts to rotate in stableconditions regardless of mounting directions of the vacuum evacuationapparatus. Since the vacuum evacuation apparatus according to thepresent invention has an appearance as a single pump unit, the user doesnot usually think that it contains the dry vacuum pump and theturbomolecular pump combined together. General dry vacuum pumps uselow-viscosity lubricating oil such as mineral oil to lubricate thebearings, and hence have certain limitations on the mounting directionsthereof. On the other hand, turbomolecular pumps have their rotationalshafts rotatably supported by ball bearings that are lubricated mainlyby grease, or non-contact bearings, so that the turbomolecular pumps arefree of limitations with respect to directions in which they aremounted. The dry vacuum pump according to the present invention uses thebearings which can support the rotational shafts without usinglow-viscosity lubricating oil such as mineral oil, and thus does notpose limitations on the mounting directions of the pump unit.

A controller for controlling the whole pump unit will be describedbelow. The first vacuum pump 1 and the second vacuum pump 2 haverespective actuators, i.e., motors. However, in the case where motorpower supplies for the motors have uniformized specifications and arehoused in one housing, common components can be used to construct asingle controller, thus downsizing the controller and reducing the costof the controller, compared to the respective controllers. Thecontroller should preferably installed on the first vacuum pump.Specifically, the dry vacuum pump is heated up to a higher temperaturethan the turbomolecular pump because of the heat generated when the dryvacuum pump compresses a gas up to the atmospheric pressure. Theturbomolecular pump has a vibration level much lower than the positivedisplacement dry vacuum pump. Accordingly, the controller having anumber of electronic precision components should be installed on theturbomolecular pump, rather than the dry vacuum pump, as theturbomolecular pump is less liable to exert unwanted thermal andvibrational effects on the controller. The controller thus installed iseffective to increase the overall reliability of the pump unit.

FIGS. 6A and 6B are front elevational views showing a vacuum evacuationapparatus with a controller 4 installed on the first vacuum pump 1.

In an example of FIG. 6A, the controller 4 is attached to an outercircumferential surface of the first vacuum pump 1.

In an example of FIG. 6B, the controller 4 is attached to a lowersurface of the first vacuum pump 1. The controller 4 may be attached tothe first vacuum pump 1 through a mount portion incorporating avibro-isolating mechanism therein. The vibro-isolating mechanism maycomprise a vibro-isolating rubber (natural rubber, nitrile rubber,silicone rubber, fluoro rubber, etc.) or a spring.

In FIGS. 6A and 6B, the controller 4 is installed on the first vacuumpump 1. However, the controller 4 may be installed in any selectedposition spaced from the first vacuum pump 1.

FIGS. 7A and 7B are cross-sectional views showing embodiments in which abottom component of the first vacuum pump 1 and a pump casing of thesecond vacuum pump 2 are integrally joined to each other.

In an example of FIG. 7A, a bottom component 40 of the first vacuum pump1 and a pump casing 50 of the second vacuum pump 2 are integrally joinedto each other to form an integral unit 60.

In an example of FIG. 7B, a bottom component 40 of the first vacuum pump1 and a pump casing 50 of the second vacuum pump 2 are integrally joinedto each other to form an integral unit 60 which has an evacuationpassage 3 a defined therein which provides fluid communication betweenthe first vacuum pump 1 and the second vacuum pump 2.

As shown in FIGS. 7A and 7B, the bottom component 40 and the pump casing50 are integrated into a common part, so that the number of parts usedis reduced and hence the cost thereof is reduced, and the overall unittakes up a reduced volume. As shown in FIG. 7B, the integral unit 60 mayincorporate the evacuation passage 3 a for the two pumps. If theevacuation path of the two pumps can be shortened, the conductance ofthe pump unit is increased, and the volume of the second vacuum pump 2can be reduced. Then, the cost of the entire pump unit can be furtherreduced and the volume taken up by the entire pump unit can be reduced.Furthermore, since the bottom component 40 and the pump casing 50 areintegrated, thermal conductivity of the two pumps can be improved. Thesecond vacuum pump 2 which compresses a gas up to the atmosphericpressure consumes more electric power and generates more heat than thefirst vacuum pump 1 at the ultrahigh vacuum side. If the second vacuumpump 2 is cooled by cooling water, the increased thermal conductivitybetween the two pumps allows only a cooling mechanism incorporated inthe first vacuum pump 1 to cool the two pumps efficiently (to radiateheat from the two pumps efficiently).

If the second vacuum pump 2 is not cooled by cooling water, then inorder to lower the thermal conductivity between the fastening surfacesof the first vacuum pump 1 and the second vacuum pump 2, it is effectiveto combine a thermal insulation with the fastening portion or to reducethe cross-sectional area of a contacting region of the fasteningportion, or both to combine a thermal insulation with the fasteningportion and to reduce the cross-sectional area of a contacting region ofthe fastening portion. If the second vacuum pump 2 is not cooled bycooling water, then it is forcedly air-cooled. As described above, thesecond vacuum pump 2 which compresses a gas up to the atmosphericpressure consumes more electric power and generates more heat than thefirst vacuum pump 1. If the second vacuum pump 2 is forcedly air-cooled,its exhaust heat performance is much lower than the cooling water. Ifthe thermal conductivity between the two pumps is high, the heat may betransferred from the second vacuum pump 2 to the first vacuum pump 1,possibly impairing the normal operation of the first vacuum pump 1.Consequently, the thermal conductivity between the two pumps is loweredto minimize the heat transfer from the second vacuum pump 2 to the firstvacuum pump 1. An air-cooling fan that is designed to match thecross-sectional area of the second vacuum pump 2 is used to locallyair-cool the second vacuum pump 2 to discharge the heat therefrom. Ifthe heat from the second vacuum pump 2 is transferred to the firstvacuum pump 1 and both the first vacuum pump 1 and the second vacuumpump 2 need to be air-cooled, then it is necessary to install the fanand to design and install a duct or cover for guiding an air flow inorder to apply the air flow efficiently to the two pumps. If only thesecond vacuum pump 2 is locally air-cooled, the installation of the fanand the designing and installation of the duct or cover are simplified.The thermal insulation material may be ceramics (alumina, yttria,zirconia, etc.), stainless steel alloy, or plastics (PEEK, PTFE, etc.).

FIG. 8 is a schematic front elevation view showing an embodiment inwhich a vibro-isolating mechanism 61 is provided between fasteningsurfaces of the first vacuum pump 1 and the second vacuum pump 2.According to the present invention, since the screw rotors 52 a, 52 b ofthe second vacuum pump 2 are capable of rotating in opposite directionsin synchronism with each other because of a magnetic coupling betweenthe magnet rotors 54, the second vacuum pump 2 does not need any timinggears for synchronizing the two screw rotors 52 a, 52 b, so that anyvibrations of the second vacuum pump 2 are greatly reduced. Even so, thesecond vacuum pump 2 which compresses a gas up to the atmosphericpressure vibrates to an extent greater than the first vacuum pump 1comprising a turbomolecular pump. Therefore, as shown in FIG. 8, thevibro-isolating mechanism 61 for isolating vibrations from the secondvacuum pump 1 is provided at the fastening portion of the first vacuumpump 1 and the second vacuum pump 2, and thus any vibrations that aretransmitted from the second vacuum pump 2 to the first vacuum pump 1 canbe reduced. The vibro-isolating mechanism 61 may comprise avibro-isolating rubber (natural rubber, nitrile rubber, silicone rubber,fluoro rubber, etc.) or a spring.

In the vacuum evacuation apparatus shown in FIG. 8, the evacuationpassage component 3 interconnecting the outlet port of the first vacuumpump 1 and the inlet port of the second vacuum pump 2 is made of avibro-isolating material. If the evacuation passage component 3 is madeof a highly rigid material or has a highly rigid structure, then it maytransmit vibrations from the second vacuum pump 2 to the first vacuumpump 1. Since the evacuation passage component 3 is made of avibro-isolating material, it can minimize vibrations transmitted fromthe second vacuum pump 2 to the first vacuum pump 1. The vibro-isolatingmaterial may be a rubber material such as natural rubber, nitrilerubber, silicone rubber or fluoro rubber, and may be in the shape of atube or a block. When a vacuum is created in the evacuation passagecomponent 3 which is made of a vibro-isolating material such as rubber,it tends to be deformed under the differential pressure between thepressure in the evacuation passage component 3 and the atmosphericpressure. Though the evacuation passage component 3 is deformed todifferent degrees depending on the material and shape thereof, a helicalspring of metal may be placed in the evacuation passage component 3 toprevent the evacuation passage component 3 from being deformed. Thehelical spring thus placed in the evacuation passage component 3 doesnot prevent the evacuation passage component 3 from being bent orcurved. The length of the helical spring may be determined as desiredrelative to the length of the evacuation passage component 3.

FIG. 9 is a schematic side elevational view showing an embodiment inwhich the first vacuum pump 1 and the second vacuum pump 2 are fastenedto each other by a fastening component combined with a vibro-isolatingmechanism. As shown in FIG. 9, a fastening component 62 is disposedbetween the first vacuum pump 1 and the second vacuum pump 2. Aplurality of vibro-isolating bushings 63 are mounted on the fasteningcomponent 62. The fastening component 62 is fixed to the first vacuumpump 1 by fastening bolts 64 that are threaded through the respectivevibro-isolating bushings 63 into the first vacuum pump 1.

The fastening component 62 has an evacuation passage 62 a definedtherein which is held in fluid communication with the inlet port SP ofthe second vacuum pump 2 and an evacuation passage 62 b defined thereinwhich is held in fluid communication with the outlet port DP of thesecond vacuum pump 2. The evacuation passage 62 a of the fasteningcomponent 62 is connected to the outlet port DP (see FIG. 2) of thefirst vacuum pump 1 by an evacuation passage component 3. The evacuationpassage 62 b of the fastening component 62 serves to vent the outletport DP of the second vacuum pump 2 to the atmosphere. The evacuationpassage component 3 is made of a vibro-isolating material such as rubberor the like.

FIGS. 10A, 10B and 10C are views showing the structure of a fasteningassembly comprising the fastening component 62 and the vibro-isolatingbushings 63. FIG. 10A is a cross-sectional view of the fasteningassembly, FIG. 10B is a bottom view of the fastening assembly, and FIG.10C is an exploded perspective view of one of the vibro-isolatingbushings 63.

As shown in FIGS. 10A and 10B, the fastening component 62 has aplurality of through holes 62 h, and flanges 62 f (see FIG. 10A)projecting radially inwardly from the inner circumferential wallsurfaces of the through holes 62 h. As shown in FIG. 10C, each of thevibro-isolating bushings 63 includes an upper member 63 a comprising alarge-diameter ring-shaped portion and a small-diameter ring-shapedportion, and a lower member 63 b comprising a ring-shaped portion. Asshown in FIG. 10A, the upper member 63 a is mounted on the fasteningcomponent 62 in such a manner that the small-diameter ring-shapedportion is fitted in a circular hole defined by the innercircumferential surface of the flange 62 f of the fastening component 62and the large-diameter ring-shaped portion having a lower surface isheld against the upper surface of the flange 62 f. The lower member 63 bis fitted over the outer circumferential surface of the small-diameterring-shaped portion of the upper member 63 a and held against the lowersurface of the flange 62 f. The fitting surfaces of the upper member 63a and the lower member 63 b are integrally united together by anadhesive bonding or the like, causing the upper member 63 a and thelower member 63 b to grip the flange 62 f of the fastening component 62.In this manner, all the vibro-isolating bushings 63 are mounted in placeon the fastening component 62. Then, the fastening bolts 64 are insertedthrough the respective vibro-isolating bushings 63, and threaded intothe first vacuum pump 1 with washers 65 interposed between the heads ofthe fastening bolts 64 and the vibro-isolating bushings 63. Therefore,the fastening component 62 is securely fastened to the first vacuum pump1 with the vibro-isolating bushings 63 disposed therebetween. Thefastening component 62 and the second vacuum pump 2 are fastened to eachother by bolts or the like.

As shown in FIGS. 10A through 10C, since the first vacuum pump 1 and thesecond vacuum pump 2 are fastened to each other using a vibro-isolatingmechanism comprising a plurality of vibro-isolating bushings 63, thelevel of vibrations that are transmitted from the second vacuum pump 2to the first vacuum pump 1 can be lowered.

FIGS. 11A and 11B are front elevation views showing embodiments in whicha pump unit (vacuum evacuation apparatus) having the first vacuum pump 1and the second vacuum pump 2 that are integrated is mounted on a vacuumcontainer (vacuum chamber) 5. In FIGS. 11A and 11B, the pump unit(vacuum evacuation apparatus) shown in FIG. 1 is mounted on the vacuumcontainer (vacuum chamber) 5.

In the embodiment shown in FIG. 11A, the pump unit which includes thefirst vacuum pump 1 and the second vacuum pump 2 that are integrallyconnected to each other is mounted on a lower surface of the vacuumcontainer 5 with the axis of the first vacuum pump 1 extendingvertically. The axes of the screw rotors 52 a, 52 b of the second vacuumpump 2 are perpendicular to the axis of the first vacuum pump 1.

In the embodiment shown in FIG. 11B, the pump unit which includes thefirst vacuum pump 1 and the second vacuum pump 2 that are integrallyconnected to each other is mounted on a side surface of the vacuumcontainer 5 with the axis of the first vacuum pump 1 extendinghorizontally. The axes of the screw rotors 52 a, 52 b of the secondvacuum pump 2 are perpendicular to the axis of the first vacuum pump 1.

The pump unit which includes the first vacuum pump 1 and the secondvacuum pump 2 that are integrally connected to each other may be mountedon an upper surface of the vacuum container 5. Further, the pump unitwhich includes the first vacuum pump 1 and the second vacuum pump 2 thatare integrally connected to each other as shown in FIGS. 5A through 5Cmay be mounted on the vacuum container 5 in the same mounting posturesas those shown in FIGS. 11A and 11B.

Another mounting posture in which the second vacuum pump 2 is mounted onthe first vacuum pump 1 will be described below.

FIGS. 12A and 12B are views showing a mounting posture in which thesecond vacuum pump 2 is mounted on a side surface of the first vacuumpump 1, FIG. 12A is a side elevational view, partly in cross section andFIG. 12B is a bottom view.

As shown in FIGS. 12A and 12B, the second vacuum pump 2 is mounted on aside surface of the first vacuum pump 1. Specifically, the first vacuumpump 1 has a cylindrical pump casing with a flat cut surface on an outercircumferential surface thereof, and the second vacuum pump 2 is fixedto the flat cut surface. In the embodiment shown in FIGS. 12A and 12B,the axis 1 x of the first vacuum pump 1 and the axes 52 ax, 52 bx of therespective screw rotors 52 a, 52 b of the second vacuum pump 2 areparallel to each other. In the embodiments shown in FIGS. 1 and 5, therotational shaft of the first vacuum pump 1 and the rotational shafts ofthe second vacuum pump 2 are perpendicular to each other to preventradial resonant vibrations from being produced. According to the presentinvention, since the screw rotors 52 a, 52 b of the second vacuum pump 2are capable of rotating in opposite directions in synchronism with eachother because of a magnetic coupling between the magnet rotors 54, thesecond vacuum pump 2 does not need any timing gears for synchronizingthe two screw rotors 52 a, 52 b, so that any vibrations of the secondvacuum pump 2 can be greatly reduced. Consequently, no significantradial resonant vibrations are not produced even though the rotationalshaft of the first vacuum pump 1 and the rotational shafts of the secondvacuum pump 2 are perpendicular to each other.

FIGS. 13A, 13B and 13C are views showing an embodiment in which thesecond vacuum pump 2 is mounted on a side surface of the first vacuumpump 1, and the first vacuum pump 1 and the second vacuum pump 2 arefastened to each other by a fastening component combined with avibro-isolating mechanism. FIG. 13A is a side elevational view, partlyin cross section, of the first vacuum pump 1 and the second vacuum pump2, FIG. 13B is a bottom view, partly in cross section, of the firstvacuum pump 1 and the second vacuum pump 2, and FIG. 13C is across-sectional view showing structural details of a fastening assemblythat fastens the first vacuum pump 1 and the second vacuum pump 2 shownin FIGS. 13A and 13B.

As shown in FIGS. 13A and 13B, the second vacuum pump 2 is mounted on aside surface of the first vacuum pump 1, and a fastening component 62 isdisposed between the first vacuum pump 1 and the second vacuum pump 2. Aplurality of vibro-isolating bushings 63 are mounted on the fasteningcomponent 62. The fastening component 62 is fixed to the first vacuumpump 1 by fastening bolts 64 that are threaded through the respectivevibro-isolating bushings 63 into the first vacuum pump 1. As shown inFIG. 13C, the fastening component 62, the vibro-isolating bushings 63,and the fastening bolts 64 are identical in structure to those shown inFIGS. 10A through 10C, and are installed in position in the same manneras shown in FIGS. 10A through 10C.

FIG. 14 is a schematic front elevation view showing an embodiment inwhich a check valve 6 is provided in an evacuation passage component 3which interconnects an outlet port of the first vacuum pump 1 and aninlet port of the second vacuum pump 2. As shown in FIG. 14, the pumpunit which includes the first vacuum pump 1 and the second vacuum pump 2that are integrally connected to each other is mounted on the vacuumcontainer 5. The check valve 6 is disposed in the evacuation passagecomponent 3 which interconnects the outlet port of the first vacuum pump1 and the inlet port of the second vacuum pump 2.

According to the present invention, the first vacuum pump 1 comprising aturbomolecular pump and the second vacuum pump 2 comprising a dry vacuumpump are integrally connected together into an integral pump unitincluding the evacuation passage component 3 therein. Therefore, thepressure conditions for the evacuation passage component 3 are known.When one of the first and second vacuum pumps 1, 2 fails to operate,e.g., when the dry vacuum pump becomes faulty in operation, the backpressure of the turbomolecular pump increases suddenly. By providing thecheck valve 6 which automatically closes under the differential pressurein the evacuation passage component, the pressure at the exhaust side ofthe turbomolecular pump can be prevented from abruptly rising.

FIG. 15 is a schematic front elevation view showing an embodiment inwhich a bypass pipe 7 interconnecting the inlet port of the first vacuumpump 1 and the inlet of the second vacuum pump 2 is provided forbypassing the first vacuum pump 1. As shown in FIG. 15, the bypass pipe7 interconnects the inlet port of the first vacuum pump 1 and the inletof the second vacuum pump 2 is provided. The bypass pipe 7 serves todirectly discharge a gas from the inlet port of the first vacuum pump 1into the inlet of the second vacuum pump 2, thereby bypassing the firstvacuum pump 1. Consequently, even when the vacuum in the vacuumcontainer 5 breaks, a sudden load buildup can be prevented from beingexerted on the first vacuum pump 1, and hence the rotating body of thefirst vacuum pump can be protected against damage.

Further, a bypass valve 8 which is opened to connect the inlet port ofthe first vacuum pump 1 directly to the inlet of the second vacuum pump2 is provided in the bypass pipe 7 in the event of an abrupt increase ofthe pressure in the vacuum container 5. The bypass valve 8 can beautomatically opened and closed under pressure conditions in the bypasspipe 7. Such pressure conditions can be established with ease becausethe bypass pipe 7 is constructed under optimum conditions between thefirst vacuum pump 1 and the second vacuum pump 2 which are integrallyconnected together into a pump unit according to the present invention.

In the above embodiments, the second vacuum pump 2 is illustrated anddescribed as a screw-type dry pump. However, the second vacuum pump 2may comprise a roots dry pump, a diaphragm pump, or a scroll pump.However, if the second vacuum pump 2 comprises a diaphragm pump, thenbecause the diaphragm pump is a pump having an evacuation principle forevacuating a gas by moving a diaphragm up and down to cause volumetricchanges, the vertically moving direction (vibrating direction) of thediaphragm and the axial direction of the first vacuum pump shouldpreferably be parallel to each other for the purpose of reducing overallvibrations of the vacuum evacuation apparatus.

Next, a controlling process of the controller which controls the firstvacuum pump 1 and the second vacuum pump 2 will be described below.

(1) Usually, the evacuation rate of a pump is controlled by adjustingthe opening area of the suction side with a control valve or the like.According to the present invention, however, the pressure in the vacuumcontainer to be evacuated is controlled by controlling at least one ofthe rotational speed of the first vacuum pump 1 and the rotational speedof the second vacuum pump 2, rather than by adjusting the opening(opening area) of a valve disposed between the vacuum container and thepump. In this manner, the evacuation rate of each of the vacuum pumps 1,2 is adjusted to adjust the overall evacuation rate of the pump systemas the vacuum evacuation apparatus. In other words, the pressure in thevacuum container can be controlled by the single pump system without theneed for a control valve other than the vacuum pumps.

(2) FIG. 16 is a set of graphs showing comparison results in which therotational speeds of first and second vacuum pumps were changed toadjust the pressure in a vacuum container in a pump rotational speedcontrol process which was performed on a vacuum evacuation apparatusaccording to the present invention and a vacuum evacuation apparatusaccording to the related art, in the case of the first vacuum pumpcomprising a turbomolecular pump and the second vacuum pump comprising adry pump.

With the vacuum evacuation apparatus according to the present invention,the piping interconnecting the first vacuum pump (turbomolecular pump)and the second vacuum pump (dry pump) is very short. After pressureadjustment in the vacuum container is started, the rotational speed ofthe first vacuum pump is lowered, and when the pressure in the vacuumcontainer reaches a certain level (start point of deceleration of thesecond pump), the second vacuum pump starts to reduce the rotationalspeed thereof. Since the piping interconnecting the first vacuum pumpand the second vacuum pump is short, the pressure in the vacuumcontainer quickly changes in response to the reduction in the rotationalspeed of the second vacuum pump. As a result, the pressure in the vacuumcontainer can reach a target pressure, i.e., the adjustment of thepressure in the vacuum container can be completed, in the shortestperiod of time. With the vacuum evacuation apparatus according to therelated art, however, since the piping interconnecting the first vacuumpump and the second vacuum pumps is longer, the pressure in the vacuumcontainer changes with a delay in response to the reduction in therotational speed of the second vacuum pump, with the result that itconsumes a certain period of time for the pressure in the vacuumcontainer to reach a target pressure.

When the first vacuum pump 1 and the second vacuum pump 2 are integrallyconnected together into an integral pump system, the second vacuum pump2 should desirably be mounted on the first vacuum pump 1. Consequently,it is desirable for the second vacuum pump 2 to have outer dimensionssmaller than those of the first vacuum pump 1.

Next, specific numerical values of the outer dimensions of the firstvacuum pump 1 and the second vacuum pump 2 will be described below. Thedimensions described below do not include those of electric componentssuch as drivers, a controller, air-cooling fans, etc., but include onlypump evacuation sections and actuators (motors).

(1) In the case where the second vacuum pump according to the presentinvention comprises a dual-shaft positive displacement pump (screwrotors) and a magnetic coupling motor, the ultimate performance that canbe achieved by the second vacuum pump is 400 Pa or lower.

TABLE 1 General General evacuation General outer General axial volumerates dimensions mm dimensions mm ratios First vacuum  100 L/s Diameter:100 110-150 1 pump 6000 L/min Second vacuum  15 L/min Width: 90 110 0.4pump

The ratio of the general evacuation rate of the second vacuum pump andthe general evacuation rate, which is assumed to be 1, of the firstvacuum pump: 1/400

The ratio of the general axial dimension of the second vacuum pump andthe general axial dimension, which is assumed to be 1, of the firstvacuum pump: 1-0.7

The ratio of the general volume of the second vacuum pump and thegeneral volume, which is assumed to be 1, of the first vacuum pump: 0.4

TABLE 2 General General evacuation General outer General axial volumerates dimensions mm dimensions mm ratios First vacuum  300 L/s Diameter:150 200-240 1 pump 18000 L/min Second vacuum   45 L/min Width: 130 1600.4 pump

The ratio of the general evacuation rate of the second vacuum pump andthe general evacuation rate, which is assumed to be 1, of the firstvacuum pump: 1/400

The ratio of the general axial dimension of the second vacuum pump andthe general axial dimension, which is assumed to be 1, of the firstvacuum pump: 0.8-0.6

The ratio of the general volume of the second vacuum pump and thegeneral volume, which is assumed to be 1, of the first vacuum pump: 0.4

(2) In the case where the second vacuum pump that can be used in theabove combination is a diaphragm pump, the ultimate performance that canbe achieved by the second vacuum pump is 400 Pa or lower.

TABLE 3 General General evacuation General outer General axial volumerates dimensions mm dimensions mm ratios First vacuum  100 L/s Diameter:100 110-150 1 pump 6000 L/min Second vacuum   5 L/min Width: 80 200 1pump

The ratio of the general evacuation rate of the second vacuum pump andthe general evacuation rate, which is assumed to be 1, of the firstvacuum pump: 1/1200

The ratio of the general axial dimension of the second vacuum pump andthe general axial dimension, which is assumed to be 1, of the firstvacuum pump: 1.8-1.3

The ratio of the general volume of the second vacuum pump and thegeneral volume, which is assumed to be 1, of the first vacuum pump: 0.4

TABLE 4 General General evacuating General outer General axial volumerates dimensions mm dimensions mm ratios First vacuum  300 L/s Diameter:150 200-240 1 pump 18000 L/min Second vacuum   20 L/min Width: 160 3302.6 pump

The ratio of the general evacuation rate of the second vacuum pump andthe general evacuation rate, which is assumed to be 1, of the firstvacuum pump: 1/900

The ratio of the general axial dimension of the second vacuum pump andthe general axial dimension, which is assumed to be 1, of the firstvacuum pump: 1.7-1.4

The ratio of the general volume of the second vacuum pump and thegeneral volume which is assumed to be 1, of the first vacuum pump: 2.6

As can be seen from the above comparison results, in the case where thefirst vacuum pump comprises a turbomolecular pump and the second vacuumpump comprises a dual-shaft positive displacement pump (screw rotors)with magnetic coupling motor, the volume of the second vacuum pump canbe smaller than the volume of the first vacuum pump, and thus there isno limitation on the mounting posture when the second vacuum pump ismounted on the first vacuum pump.

As a turbomolecular pump and a dual-shaft positive displacement pump areused respectively as the first vacuum pump and the second vacuum pump,it is possible to integrally connect a plurality of second vacuum pumpsto the first vacuum pump which has an evacuation capacity that isseveral times greater than each of the second vacuum pumps.

FIG. 17 is a schematic view showing a vacuum evacuation apparatusaccording to an embodiment of the present invention, which includes asingle first vacuum pump 1 and a plurality of second vacuum pumps 2integrally connected to the first vacuum pump 1. As shown in FIG. 17,the two second vacuum pumps 2 are integrally connected to the singlefirst vacuum pump 1. The outlet port of the first vacuum pump 1 isconnected to the inlet ports of the second vacuum pumps 2 by respectiveindividual evacuation passage components 3. Since the plural secondvacuum pumps 2 are integrally connected to the single first vacuum pump1, it is possible to construct a roughing pump system having anevacuation capacity which matches the evacuation capacity of the firstvacuum pump 1.

FIG. 18 is a schematic view showing a vacuum evacuation apparatusaccording to an embodiment of the present invention, which includes asingle first vacuum pump 1 and a plurality of second vacuum pumps 2integrally connected to the first vacuum pump 1 by evacuation passages.As shown in FIG. 18, the two second vacuum pumps 2 are integrallyconnected to the single first vacuum pump 1, providing an integral pumpunit that is mounted on a lower surface of the vacuum container 5. Theoutlet port of the first vacuum pump 1 is connected to the inlet portsof the second vacuum pumps 2 by an evacuation passage component 3. Sincethe plural second vacuum pumps 2 are integrally connected to the singlefirst vacuum pump 1, it is possible to construct a roughening pumpsystem having an evacuation capacity which matches the evacuationcapacity of the first vacuum pump 1.

Inasmuch as the two second vacuum pumps 2 are connected in a parallellayout to the single first vacuum pump 1, the second vacuum pumps 2 havetheir overall evacuation capacity doubled. When the pressure control inthe vacuum container is performed, the two parallel second vacuum pumps2 can control the pressure in the vacuum container 5 more finely andquickly than a single second vacuum pump 2.

If a single second vacuum pump 2 is used, a failure of the second vacuumpump 2 leads to a shutdown of the first vacuum pump 1, resulting in aquick pressure buildup in the vacuum container 5. However, in the casewhere the vacuum evacuation apparatus includes the two second vacuumpumps 2, even if one of the second vacuum pumps 2 fails to operate, theother second vacuum pump 2 operates to keep the pressure in the outletport of the first vacuum pump 1 below an allowable pressure level.Therefore, a situation where the first vacuum pump 1 shuts down to causea quick pressure buildup in the vacuum container 5 can be avoided.

FIG. 19 is a schematic view showing a vacuum evacuation apparatusaccording to an embodiment of the present invention, which includes aplurality of first vacuum pumps 1 and a single second vacuum pump 2which are integrally connected by evacuation passages. As shown in FIG.19, two parallel first vacuum pumps 1 and a single second vacuum pump 2are integrally connected together into an integral pump unit that ismounted on a lower surface of the vacuum container 5. The outlet portsof the two first vacuum pumps 1 and the inlet port of the second vacuumpump 2 are interconnected by an evacuation passage component 3. In thismanner, the plural first vacuum pumps 1 and a single second vacuum pump2 are integrally connected together into an integral pump unit, andhence each of the first vacuum pumps 1 is reduced in size.

With the two parallel first vacuum pumps 1 and the single second vacuumpump 2 being integrally connected together, it is not necessary for eachof the first vacuum pumps to have a large-size pump rotor which rotatesat a high speed for an increased evacuation capacity. Therefore, a safevacuum evacuation system can be constructed.

FIG. 20 is a block diagram of a control circuit for controlling a vacuumevacuation apparatus including two first vacuum pumps 1 and a singlesecond vacuum pump 2 which are integrally connected into an integralpump unit. As shown in FIG. 20, the control circuit includes a motor forone of the two first vacuum pumps 1, i.e., TMP (turbomolecular pump) 1,a motor for the other first vacuum pump 1, i.e., TMP2, an inverter (INV)for the TMP1, an inverter (INV) for the TMP2, a motor for the secondvacuum pump 1, i.e., a DRY (dry) pump, and an inverter (INV) for the DRYpump. The control circuit also includes a single controller (CPU) forintegrally controlling the three inverters, i.e., the INV for the TMP1,the INV for the TMP2, and the INV for the DRY pump. The CPU is capableof optimally controlling the pressure in the vacuum container bycontrolling the rotational speeds of the motors of the first and secondvacuum pumps 1, 2 at desired rotational speed control rates with theinverters without the need for pressure detectors in the evacuationpipes connected to the first and second vacuum pumps 1, 2. The controlcircuit shown in FIG. 20 also includes a power factor controller (PFC)and a DC/DC converter (DC/DC).

FIG. 21 is a graph showing how the rotational speeds of a single firstvacuum pump and two second vacuum pumps were changed to adjust thepressure in a vacuum container in a pump rotational speed controlprocess which was performed on a vacuum evacuation apparatus accordingto the present invention, in the case of the first vacuum pumpcomprising a turbomolecular pump and the two second vacuum pumpscomprising a dry pump.

With the single first vacuum pump (turbomolecular pump) and the twosecond vacuum pumps (dry pumps) being integrally connected together byevacuation passages, after pressure adjustment in the vacuum containeris started, the rotational speed of the first vacuum pump is lowered,and when the pressure in the vacuum container rises, one of the secondvacuum pumps starts to reduce the rotational speed thereof. At thistime, the first vacuum pump continues speed reduction. After the firstvacuum pump has stopped reducing its rotational speed, the other secondvacuum pump starts to reduce the rotational speed thereof. Then, thesecond vacuum pump which has started reducing its rotational speedearlier stops reducing its rotational speed. The other second vacuumpump continuously reduces its rotational speed, and when the pressure inthe vacuum container reaches a desired pressure level, the other secondvacuum pump stops reducing its rotational speed. At this time, thepressure adjustment in the vacuum container is completed.

Since the three vacuum pumps are interconnected, the pressure in thevacuum container changes quickly in response to the reduction in therotational speeds of the second vacuum pumps, and thus the pressure inthe vacuum container can reach a target pressure (pressure adjustmentcompleting point), in the shortest period of time. In addition, sincethe two second vacuum pumps start and stop reducing their rotationalspeeds at different times, the pressure in the vacuum container can beadjusted finely.

FIGS. 22 through 25 are schematic cross-sectional views showing variousdifferent turbomolecular pumps for use in the vacuum evacuationapparatus according to the present invention.

As shown in FIG. 22, the first vacuum pump 1 comprises a turbomolecularpump having a pump casing 109, and rotor blades 111 and stator blades114 that are alternately mounted on a rotational shaft 113 and arrangedsuccessively from a central inlet port defined in the pump casing 109toward left and right opposite ends of the rotational shaft 113. Themultistage rotor blades 111 are integrally formed on the rotationalshaft 113, and the multistage stator blades 114 are fixed to the pumpcasing 109.

A second vacuum pump 2 that is integrally connected to the first vacuumpump 1 is structurally identical to the screw-type dry vacuum pump shownin FIG. 3.

The second vacuum pump 2 has a pair of parallel screw rotors which areparallel to a lower surface of the first vacuum pump 1. The screw rotorshave respective axes parallel to the axis of the rotational shaft 113 ofthe first vacuum pump 1.

FIG. 23 shows a different posture when the second vacuum pump 2 ismounted on the first vacuum pump 1.

As shown in FIG. 23, the axes of the screw rotors of the second vacuumpump 2 are perpendicular to the axis of the rotational shaft 113 of thefirst vacuum pump 1, and extend parallel to each other and are spaced bya common distance from the lower surface of the first vacuum pump 1.

FIG. 24 shows a vacuum evacuation apparatus in which the fasteningcomponent 62 and the vibro-isolating bushings 63 shown in FIGS. 9 and 10are disposed between the first vacuum pump 1 and the second vacuum pump2 shown in FIG. 22.

FIG. 25 shows a vacuum evacuation apparatus in which the fasteningcomponent 62 and the vibro-isolating bushings 63 shown in FIGS. 9 and 10are disposed between the first vacuum pump 1 and the second vacuum pump2 shown in FIG. 23. As shown in FIGS. 24 and 25, since the first vacuumpump 1 and the second vacuum pump 2 are fastened to each other using avibro-isolating mechanism including the vibro-isolating bushings 63, thelevel of vibrations that are transmitted from the second vacuum pump 2to the first vacuum pump 1 can be lowered.

Although preferred embodiments have been described in detail above, itshould be understood that the present invention is not limited to theillustrated embodiments, but many changes and modifications can be madetherein without departing from the appended claims.

What is claimed is:
 1. A vacuum evacuation apparatus for evacuating acontainer from an atmospheric pressure to a high vacuum or less,comprising: a first vacuum pump for evacuating the container to a highvacuum or less; and a second vacuum pump for evacuating the containerfrom an atmospheric pressure to a medium or low vacuum; wherein saidfirst vacuum pump and said second vacuum pump are integrally connectedto each other into an integral unit.
 2. A vacuum evacuation apparatusaccording to claim 1, wherein said first vacuum pump has a rotationalshaft and said second vacuum pump has a rotational shaft, and saidrotational shaft of said first vacuum pump and said rotational shaft ofsaid second vacuum pump have respective axes which are perpendicular toeach other.
 3. A vacuum evacuation apparatus according to claim 1,wherein said first vacuum pump has a rotational shaft and said secondvacuum pump has a rotational shaft, and said rotational shaft of saidfirst vacuum pump and said rotational shaft of said second vacuum pumpare rotatably supported by one of self-lubricating bearings, bearingshaving a semi-solid lubricant or a solid lubricant therein, gasbearings, and magnetic bearings; and wherein said rotational shaft ofsaid first vacuum pump and said rotational shaft of said second vacuumpump are rotatable regardless of directions in which said first vacuumpump and said vacuum pump are installed.
 4. A vacuum evacuationapparatus according to claim 1, wherein said first vacuum pump has abottom component and said second vacuum pump has a casing, and saidbottom component and said casing are integrally connected to each other,thereby integrally connecting said first vacuum pump and said secondvacuum pump.
 5. A vacuum evacuation apparatus according to claim 1,wherein said first vacuum pump and said second vacuum pump areintegrally connected to each other through a heat insulation member or asmall area of contact.
 6. A vacuum evacuation apparatus according toclaim 1, wherein said first vacuum pump and said second vacuum pump areintegrally connected to each other through a vibro-isolating mechanism.7. A vacuum evacuation apparatus according to claim 1, wherein saidfirst vacuum pump has an outlet port and said second vacuum pump has aninlet port, and said outlet port and said inlet port are interconnectedby an evacuation passage component comprising a vibro-isolatingmaterial.
 8. A vacuum evacuation apparatus according to claim 1, whereinsaid first vacuum pump has an inlet port and said second vacuum pump hasan inlet port, and said inlet port of said first vacuum pump and saidinlet port of said second vacuum pump are interconnected by a bypasspassage for bypassing said first vacuum pump.
 9. A vacuum evacuationapparatus according to claim 1, wherein said first vacuum pump has anoutlet port and said second vacuum pump has an inlet port, and saidoutlet port and said inlet port are interconnected by an evacuationpassage component incorporating therein a check valve for preventing afluid from flowing back from said second vacuum pump to said firstvacuum pump while said first vacuum pump is in operation.
 10. A vacuumevacuation apparatus according to claim 1, further comprising: acontroller for controlling said first vacuum pump and said second vacuumpump; wherein said controller is integrally connected to said firstvacuum pump or is installed separately from said first vacuum pump. 11.A vacuum evacuation apparatus according to claim 10, wherein when eachof said first vacuum pump and said second vacuum pump reaches a ratedrotational speed and no gas is introduced into the container, saidcontroller lowers a voltage applied to a motor of at least one of saidfirst vacuum pump and said second vacuum pump and continuously operatessaid motor at a motor maximum efficient point.
 12. A vacuum evacuationapparatus according to claim 10, wherein said controller is capable ofcontrolling the pressure in the container at a target pressure level byindividually controlling respective rotational speeds of said firstvacuum pump and said second vacuum pump depending on flow rates of thegas evacuated therefrom.
 13. A vacuum evacuation apparatus according toclaim 1, wherein said first vacuum pump comprises a turbomolecular pump,and said second vacuum pump comprises a dry vacuum pump.
 14. A vacuumevacuation apparatus according to claim 1, wherein said second vacuumpump comprises a dry vacuum pump having a pair of pump rotors withrespective magnet rotors mounted thereon, said magnet rotors have equalnumbers of magnetic poles and are disposed so that their differentmagnetic poles are magnetically attracted to each other, and currentssupplied to a multiphase armature including an iron core and a pluralityof windings disposed radially outwardly of at least one of said magnetrotors are switched to actuate said at least one of said magnet rotorsfor thereby rotating said pump rotors in opposite directions insynchronism with each other.
 15. A vacuum evacuation apparatus accordingto claim 1, wherein one of said first vacuum pump and said second vacuumpump comprises a single vacuum pump and the other of said first vacuumpump and said second vacuum pump comprises either a single vacuum pumpor a plurality of vacuum pumps.
 16. A vacuum evacuation apparatusaccording to claim 15, wherein said first vacuum pump and said secondvacuum pump are integrally connected to each other by at least oneevacuation passage.
 17. A vacuum evacuation apparatus according to claim1, wherein the ratio of an axial dimension of said second vacuum pumpand an axial dimension, which is assumed to be 1, of said first vacuumpump is in a range from 1 to 0.6, and the ratio of a volume of saidsecond vacuum pump and a volume, which is assumed to be 1, of said firstvacuum pump is in a range from 0.3 to 0.5.